1. Field of the Invention
This invention relates to a pressure-sensitive adhesive tape, more particularly, a tape having a biaxially-oriented backing, and a process for preparing pressure-sensitive adhesive tapes.
2. Discussion of the Art
Normally tacky, pressure-sensitive adhesive tapes comprise a backing bearing on at least one major surface thereof a layer of pressure-sensitive adhesive. Pressure-sensitive adhesive tapes are usually prepared by a process in which a layer of pressure-sensitive adhesive is applied to one major surface of a backing and, optionally, a layer of low-adhesion backsize composition is applied to the other major surface of the backing. Preferred adhesives include rubber-based adhesives, which consist of a blend of natural or synthetic rubber and tackifier resin. While other resins and additives can also be included, the rubber and tackifier resin are essential. Conventional rubber-based adhesives do not adhere satisfactorily to most backings made from polymeric film, particularly polyolefin and poly(vinyl chloride). Although the use of thermoplastic-elastomeric block copolymers in the rubber constituent can provide improved anchorage to backings, special formulations are generally required, and, even then, high levels of anchorage may not be attainable with some polymeric films. Improved anchorage can be brought about through the use of primers, i.e., materials capable of adhering well to both the backing and the adhesive, or other treatments, to assure a high level of anchorage of the adhesive to the backing.
At present, pressure-sensitive adhesive tapes are typically manufactured by a process comprising the steps of:
(1) providing a biaxially-oriented polymeric backing;
(2) corona treating the major surfaces of the backing to improve the adhesion of the backing to subsequently applied coatings;
(3) applying a layer of pressure-sensitive adhesive to one major surface of the backing;
(4) applying a layer of low-adhesion backsize composition to the other major surface of the backing; and
(5) winding the coated backing onto a jumbo roll, where it is stored until further converting is desired.
Japanese Patent Publication 46-21120 discloses a process for preparing a pressure-sensitive adhesive tape comprising the steps of (1) melt extruding a thermoplastic synthetic resin and an adhesive component separately as two flows; (2) guiding the two flows in a molten state to a single die to form a single fluid body comprising the thermoplastic synthetic resin at an inner wall and the adhesive component at an external wall; (3) extruding the single fluid body from the die; and (4) winding the tape in a roll-form. The adhesive component can contain a natural or synthetic rubber and a tackifier.
U.S. Pat. No. 4,379,806 (Korpman) discloses a pressure-sensitive adhesive tape comprising an adhesive layer of a normally tacky thermoplastic pressure-sensitive rubber resin, a backing layer of a normally non-tacky thermoplastic film, and an intermediate interlocking layer containing both components in a laminar relationship formed by coextruding an adhesive composition and a thermoplastic film-forming composition. The adhesive composition comprises (i) an elastomeric component and (ii) a tackifier resin component. The elastomeric component of the adhesive composition comprises an A-B-A block copolymer, A-B block copolymer, or mixtures thereof.
U.S. Pat. No. 4,513,028 (Aritake) discloses a process for producing an adhesive tape which comprises (1) forming an adhesive layer on one side of a base sheet of a polypropylene resin and a surface layer of a polypropylene resin having a melting point lower than that of the polypropylene resin of the base sheet and containing fine inorganic filler particles on the other side of the base sheet to obtain an unstretched laminated sheet, (2) stretching the laminated sheet at a temperature of at least the melting point of the polypropylene resin of the surface layer such that the thickness of the surface layer is not more than the maximum diameter of the particles it contains.
Japanese Patent Publication (Tokko): Hei 1 (1989) - 28793 discloses a method for producing an adhesive tape comprising the steps of laminating a modified polyolefin layer containing 0.01-10% by weight of unsaturated carboxylic acid or the anhydride thereof to one surface of a base polypropylene sheet, coating the modified polyolefin layer with a layer of a mixture of reactive acrylic adhesive and crosslinking agent, and subsequently heating and stretching the laminated sheet. It is stated that, if necessary, a back-side treating agent can be coated on the back surface of the polypropylene base sheet, preferably prior to the stretching step.